Conventional hydraulic operators for pipeline valves are operated automatically by a fluid storage supply subjected to pipeline pressure when there is a substantial drop in pipeline pressure due, for example, to a line break which normally causes closure of the valve, and a stand-by hand pump is provided for manually operating the valve by using the fluid storage supply when the line pressure has failed. However, if a pressure surge occurs in the pipeline when the pump is being set for manual operation or is being operated, the effect of the pressure surge on the fluid storage supply may be to throw the pump handle outwardly with great force, thereby subjecting the people in the vicinity to great danger and injury.
U.S. Pat. No. 3,089,430 discloses a rotary control valve for such a hand pump having a safety shut-off located in the suction line to the pump, and the safety shut-off constitutes a piston which is exposed to atmospheric pressure and operates by differential pressure to close the suction line in the event of a pressure surge in the pipeline. This construction had the drawback that due to the exposure of the safety shut-off piston to the atmosphere, it often became corroded or was painted over so that it did not operate quickly enough to function properly.
This defect was recognized in U.S. Pat. No. 3,911,678, and a wholly enclosed shut-off piston was provided in the same type of rotary control valve to avoid the difficulties resulting from exposing the piston to the atmosphere. While those difficulties were overcome by this later construction, it was found in actual practice that under certain conditions there was still danger of the handle of the pump flying upwardly with great force. For example, if there is pressure left in the ram of the hand pump the pump handle still may fly upwardly as the control valve is changed from either extreme position to neutral position.